On 23-Dec-25 3:43 AM, Gustavo Sousa wrote:
On Xe3_LPD, there is no instruction to program the CD2X divider anymore
and the hardware is expected to always use the default value of 0b00,
meaning "divide by 1".
With that, the CDCLK_CTL register was changed so that:
(1) The field "CD2X Divider Select" became a debug-only field.
Because we are programming CDCLK_CTL with a direct write instead
of read-modify-write operation, we still need to program "CD2X
Divider Select" in order to keep the field from deviating from its
default value. Let's, however, throw a warning if we encounter a
CDCLK value that would result in an unexpected value for that
field.
(2) The field "CD2X Pipe Select" has been removed. In fact, some
debugging in a PTL machine showed that such field comes back as
zero after writing a non-zero value to it. As such, do not
program it starting with Xe3_LPD.
Bspec: 68864, 69090
Signed-off-by: Gustavo Sousa <[email protected]>
---
drivers/gpu/drm/i915/display/intel_cdclk.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c
b/drivers/gpu/drm/i915/display/intel_cdclk.c
index 0aa59d624095..684b8437951b 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -1933,6 +1933,8 @@ static u32 bxt_cdclk_cd2x_pipe(struct intel_display
*display, enum pipe pipe)
static u32 bxt_cdclk_cd2x_div_sel(struct intel_display *display,
int cdclk, int vco, u16 waveform)
{
+ u32 ret;
+
/* cdclk = vco / 2 / div{1,1.5,2,4} */
switch (cdclk_divider(cdclk, vco, waveform)) {
default:
@@ -1941,14 +1943,27 @@ static u32 bxt_cdclk_cd2x_div_sel(struct intel_display
*display,
drm_WARN_ON(display->drm, vco != 0);
fallthrough;
case 2:
- return BXT_CDCLK_CD2X_DIV_SEL_1;
+ ret = BXT_CDCLK_CD2X_DIV_SEL_1;
+ break;
case 3:
- return BXT_CDCLK_CD2X_DIV_SEL_1_5;
+ ret = BXT_CDCLK_CD2X_DIV_SEL_1_5;
+ break;
case 4:
- return BXT_CDCLK_CD2X_DIV_SEL_2;
+ ret = BXT_CDCLK_CD2X_DIV_SEL_2;
+ break;
case 8:
- return BXT_CDCLK_CD2X_DIV_SEL_4;
+ ret = BXT_CDCLK_CD2X_DIV_SEL_4;
+ break;
}
+
+ /*
+ * On Xe3_LPD onward, the expectation is to always have
+ * BXT_CDCLK_CD2X_DIV_SEL_1 as the default.
+ */
+ if (DISPLAY_VER(display) >= 30)
+ drm_WARN_ON(display->drm, ret != BXT_CDCLK_CD2X_DIV_SEL_1);
+
+ return ret;
}
static u16 cdclk_squash_waveform(struct intel_display *display,
@@ -2136,7 +2151,9 @@ static u32 bxt_cdclk_ctl(struct intel_display *display,
waveform = cdclk_squash_waveform(display, cdclk);
- val = bxt_cdclk_cd2x_div_sel(display, cdclk, vco, waveform) |
+ val = bxt_cdclk_cd2x_div_sel(display, cdclk, vco, waveform);
+
+ if (DISPLAY_VER(display) < 30)
bxt_cdclk_cd2x_pipe(display, pipe);
Hey Gustavo,
Please update this line, function’s return value should be ORed with val.
i.e. val |= bxt_cdclk_cd2x_pipe(display, pipe);
BR,
Dnyaneshwar
/*
---
base-commit: f2a0e58c77845e1a5cb6c549dc02b2670042e588
change-id: 20251222-xe3_lpd-no-cd2x-divider-48f9f0972f98
Best regards,
--
Gustavo Sousa <[email protected]>
